We thank Dr. LaBan for his interest in our article. He raises two questions requiring a response and one minor modification.

First, he asks “why are some more vulnerable to this injury than others?” We contend that some people have tendon and bone anatomy that results in the two structures rubbing against each other in such a way as to cause injury. Factors that come into play are the size and shape of the epicondyle and the capitellum, and the site of the attachment of the extensor complex.

Second, he states that the anatomic variation between bone and tendon may be the terminal consequence (expanded via email as the “accident waiting to happen”) in the cause of tennis elbow. If we understand his question, then we agree that these underlying anatomic relationships only lay the foundation for the development of tennis elbow. Another requirement is that the elbow must be moved while the wrist extensors are under tension. If a person with a predisposing anatomic variation never puts his/her elbow/wrist extenesors to substantial use then he/she is unlikely to develop the disorder.

We found no change in the extent or type of rubbing of tendon on bone due to shoulder position.

In regard to the last sentence in his first paragraph, our hypothesis is that the tendon is weakened by the transverse rubbing (trauma) of the tendon on bone. Other authors cited in our paper, not us, described tendinous microtears from longitudinal overload as the source of tennis elbows.(1). We propose that once the tendon is weakened, tension plus abrasion causes further damage as occurs in any tendon exposed to attritional wear.

Reference:

1. Nirschl RP. Tennis Elbow. Ortho Clinics NA 1973;4:787-800.

To The Editor:

We read with interest the article by Bunata et al.(1)which called attention to the anatomic relationship of the extensor digitorum brevis and the capitellum as one of the precipitating causes of lateral epicondylitis(“tennis elbow”). This syndrome, like that of carpal tunnel and De Quervains tenosynovitis among others, usually results from “overuse”. As such, form and function are inseparable with respect to pathogenesis.

But even when controlling for age, job description, speed, and repetition of task, why are some more vulnerable to this injury than others? As a “mechanically induced condition” anatomic variation between bone and tendon may, in-fact, be a terminal consequence rather than the “initial step in the cause of tennis elbow. Remote alterations in proximal as well as distal joint biomechanics acting repetitively on the elbow through an altered kinetic chain may instead be the progenitor of the lateral epicondylitis. In this regard, LaBan, Iyer, and Tamler called attention to the frequent presence of ipsilateral restricted shoulder range of motion, especially internal rotation, in patients presenting with symptoms of tennis elbow(2). As a consequence, excessive wrist flexion is required to compensate for the proximal restricted arc of shoulder internal rotation. The extensor digitorum longus and brevis are two-joint muscles which cross both the elbow and the wrist. As such, they have the capacity under load of functionally reversing their origin insertions from a concentric/shortening to an eccentric/elongating contraction. As the muscles in mid-cycle precipitously reverse their direction, aging muscle with its reduced elastic modulus may not be “fast enough” to absorb the force of recoil. Instead, the shock of this action is primarily absorbed at the origin of the extensor expansion. With repeated trauma tendinous microtears as described by the authors can develop at the lateral epicondyle.

In the late 19th century, Epicondylitis lateralis humeri was described as a “lesion which is imperfectly recognized, [and] is sure to find a host of wanted remedies”(3). Over a hundred years later, who would argue?

The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated .

REFERENCES:

1. Bunata RE, Brown DS, Capelo R. Anatomic factors related to the cause of tennis elbow. J Bone Joint Surg Am. 2007; 89:1955-63.

2. LaBan, MM, Iyer R, Tamler MS. Occult periarthrosis of the shoulder. A possible progenitor of tennis elbow. Am J Phys Med Rehabil 2005; 84:1-4.

3. Tennis elbow: Annotations Lancet 1885; 2:772.